PURPOSE: To make it possible to form copper wirings, which are strong against an electro-migration and a stress migration and is high in reliability, easily and with high accuracy by a method wherein an etching of a copper film is performed by an ion milling method using the mixed ion beam of oxygen and argon, readhered materials are removed with an acid and the like.

CONSTITUTION: Copper wirings of a semiconductor device are formed in such a way that a process for applying a copper film 3 on the whole surface of a semiconductor substrate 1, a process for forming a mask film 12 consisting of a material different from copper on the whole surface, a process that the film 12 is etched using a photoresist film 4b of a prescribed pattern as a mask by a photolithography technique and a wiring mask 13 is formed, a process for performing an etching of the film 3 by an ion milling method using the mixed ion beam of oxygen and argon and a process for removing readhering materials 7a during the above ion milling process with an acid are included in the formation method of the copper wirings. For example, an etching of a copper film 3 is performed by an ion milling method using the mixed ion beam of 5 to 10% of oxygen and 90 to 95% of argon using a mask 13 for wiring consisting of a silicon nitride film 12. Then, readhering materials 7a on the side surfaces of the mask 13 and the like are removed by a dilute sulfuric acid treatment.